This invention relates generally to gas turbine engine nozzles and more particularly, to methods and apparatus for cooling gas turbine engine nozzles.
Gas turbine engines include combustors which ignite fuel-air mixtures which are then channeled through a turbine nozzle assembly towards a turbine. At least some known turbine nozzle assemblies include a plurality of nozzles arranged circumferentially within the engine downstream from the combustors. Each nozzle includes an airfoil vane that extends between integrally-formed inner and outer band platforms. The nozzles are cooled by a combination of internal convective cooling and gas side film cooling.
Each nozzle includes a pair of sidewalls that are connected at a leading edge and a trailing edge. The metal temperature distribution of a typical vane airfoil is such that the trailing edge is significantly hotter than a temperature of the bulk of the airfoil. The temperature gradient created results in high compressive stress at the vane trailing edge, and the combination of high stresses and high temperatures generally results in the vane trailing edge being the life limiting location of the nozzle. Accordingly, within at least some known nozzles, the airfoil vane trailing edge is cooled by a film of cooling air discharged from an internally-defined vane cavity. More specifically, the film of cooling air is discharged through trailing edge slots formed on the airfoil vane pressure side, and upstream from the airfoil vane trailing edge.
The amount of air supplied to each nozzle vane is attempted to be optimized to lessen the effect on engine performance decrement that may be associated with cooling flow extraction. Generally, the slots are formed with a length that facilitates optimizing an amount of cooling flow supplied to the trailing edge. Because of the slot length, such slots are typically manufactured using an electrical discharge machining (EDM) process. However, such a manufacturing process may increase manufacturing costs and times, and because of the complexity of the task may cause airfoil vanes to be reworked. A nozzle design including an internal cooling geometry that is comparable with the investment casting process generally is less expensive to manufacture relative to a nozzle design that requires the EDM process to produce the slots.
In one aspect, a method for fabricating a nozzle for a gas turbine engine is provided. The nozzle includes an airfoil. The method comprises forming the airfoil to include a suction side and a pressure side connected at a leading edge and a trailing edge, forming a plurality of slots in the pressure side of the airfoil extending towards the trailing edge, and extending a plurality of pins arranged in rows between the airfoil suction and pressure sides, such that at each of a first row of pins has a substantially elliptical cross-sectional area, wherein the first row of pins is between the remaining rows of pins and the airfoil pressure side slots.
In another aspect of the invention, a turbine nozzle for a gas turbine engine is provided. The nozzle includes an airfoil vane including a first wall, a second wall, and a plurality of pins extending therebetween. The first and second walls are connected at a leading edge and a trailing edge. The first wall includes a plurality of slots that extend towards the trailing edge. The plurality of pins include at least a first row of pins which have a substantially elliptical cross-sectional area. The first row of pins is positioned between the remaining plurality of pins and the first wall slots.
In a further aspect, an airfoil for a gas turbine engine nozzle is provided. The airfoil includes a root, a tip, a plurality of pins, a convex sidewall and a concave sidewall connected at a trailing edge. Each of the sidewalls extends between the root and tip. The convex sidewall defines a pressure side of the airfoil and includes a plurality of slots that extend towards the trailing edge. The plurality of pins include at least a first row of pins and a second row of pins. The first row of pins are concentrically aligned radially and each of the first row pins has a substantially elliptical cross sectional profile and is tapered such that an upstream side of each first row pin has a width that is greater than a downstream side of each first row pin. The slots are adjacent to and downstream from the first row of pins.